This invention relates to an ignition system for a two cycle engine and more particularly to an improved ignition system for a direct injected internal combustion engine.
The advantages of direct cylinder injection as opposed to manifold injection or carburetion are well known. By employing direct cylinder injection, it is possible to operate the engine at leaner mixtures than with other types of charge forming systems, particularly at low, light and medium loads. The reason for this is the direct cylinder injection permits the use of a stratified or laminar type of combustion wherein a stoiciometric fuel/air mixture is disposed only within a limited area of the combustion chamber at the time combustion begins. With other types of charge forming systems, it is substantially necessary to provide a homogeneous stoiciometric charge completely within the combustion chamber regardless of the load or operating condition. These advantages are particularly important with two cycle internal combustion engines due to the fact that the porting of these engines can give rise to the loss of unburned hydrocarbons through the exhaust port when a homogeneous mixture is inducted into the engine.
However, when a stratified charge is present in the combustion chamber and the engine is spark ignited, it is necessary to insure that the fuel/air mixture is in the vicinity of the spark gap at the time the spark plug is fired. If it is not, either incomplete combustion or no firing at all may result. Of course, it can be insured that the complete mixture will be ignited if multiple spark plugs or multiple spark firings are employed. However, the use of multiple spark plugs gives rise to a complicated cylinder head and also added costs. The use of multiple firing of the spark plug gives rise to other problems. First, a relatively complicated ignition system is necessary and by firing the spark plug a multiple number of times for each revolution of the engine undue heat can be generated in the ignition system causing premature failure.
The problems aforenoted are particularly aggravated when capacitor discharge ignition systems (CDI) are employed, as are desirable with two cycle engines. A capacitor discharge ignition system, although it has the advantages of high initial energy, has a shorter spark duration than a breaker type ignition system. As a result of this shorter spark period, the problems of making sure that the spark plug fires when a charge is in connect with its gap become greater. However, capacitor discharge ignition systems are particularly useful with two cycle engines because their high energy level will insure that deposits are burned off of the spark plug.
It is, therefore, a principal object to this invention to provide an improved ignition system for an internal combustion engine.
It is a further object to this invention to provide an ignition system that will insure firing of a stratified charge but which will not consume excessive spark energy when not required.
It is a further object to this invention to provide an ignition system for an internal combustion engine that senses when there is a homogeneous mixture in the cylinder and when there is a stratified charge and fires the spark plug accordingly so as to insure ignition under all circumstances.